Exercise treadmills are widely used for various purposes. Exercise treadmills are, for example, used for performing walking or running aerobic-type exercise while the user remains in a relatively stationary position, further, exercise treadmills are used for diagnostic and therapeutic purposes. For all of these purposes, the person on the exercise treadmill normally performs an exercise routine at a relatively steady and continuous level of physical activity. Examples of such treadmills are illustrated in U.S. Pat. Nos. 4,635,928, 4,659,074, 4,664,371, 4,334,676, 4,635,927, 4,643,418, 4,749,181, 4,614,337, 6,095,951 and 6,572,512.
Exercise treadmills typically have an endless running surface which is extended between and movable around two substantially parallel pulleys at each end of the treadmill. The running surface usually includes a belt made of a flexible material extended around the pulleys. A drive unit rotating one of the pulleys normally drives the belt. The speed of the drive unit is adjustable by the user through a set of user controls so that the level of exercise can be adjusted to simulate running or walking as desired.
The belt is typically supported by a deck or support surface beneath the upper surface of the belt. The deck is usually composed of wood or MDF, in order to provide the required support. In addition, a low-friction sheet or laminate is usually provided on the upper deck surface to reduce the friction between the deck and the belt. In most cases, decks are relatively rigid which can result in high impact loads on the user's feet, ankles and knees as the user's feet contact the belt and the deck. Users often perceive this as being uncomfortable and further can result in unnecessary damage to joints as compared to running on a softer surface.
Because the typical treadmill has a very stiff, hard running surface and can become uncomfortable for extended periods of running, manufacturers have sought to make the running surface more resilient in an attempt to improve user comfort. U.S. Pat. Nos. 3,408,067, 4,350,336, 4,616,822, 4,844,449, 5,279,528, 5,441,468, 5,454,772 and 6,095,951 disclose examples of resilient deck support on treadmills to reduce impact loads. While generally successful at reducing impact loads, these approaches have certain disadvantages. In particular, it has been found that there is a substantial advantage in being able to vary the stiffness of the decks in treadmills to accommodate the desires or running styles of different users. As a result there have been a number of attempts to provide mechanisms for varying deck stiffness, examples of which are illustrated in U.S. Pat. Nos. 4,350,336, 6,623,407, and 6,821,230. However, these approaches suffer from a number of disadvantages. In the example described in U.S. Pat. No. 4,350,336, the location of two resilient support members can be changed but this results in uneven flexing of the deck along its length. In other cases, specially designed resilient members are used that are moved or rotated into position below the deck or complex mechanisms are required to implement user variation of deck flexibility. Moreover, these approaches do not provide a method for easy or inexpensive modification of an existing treadmill design to allow the user to vary deck flexibility or support.